A police review of anti-vaccination Facebook groups prior to the Parliament protests found many had been infiltrated by fake accounts from overseas which spewed disinformation.
The police Open Source Intelligence Team (Osint) completed a month-long intelligence collection project on October 8 last year.
The Osint team uses publicly available online information for intelligence purposes.
The collection summary was released under the Official Information Act. Titled "Inauthentic account presence in anti-vaccination Facebook groups," it was classified as "in confidence".
The summary looked at three anti-vaccination Facebook groups created between December 2020 and June last year, which boasted 2600, 11,300, and 29,500 members.
The groups grew quickly during the pandemic, but they appear to have been removed from Facebook since the summary was compiled.
Several hundred accounts from each group were analysed, of which 18% were assessed as likely being inauthentic. Some were clearly accounts that had been stolen and repurposed.
Of the inauthentic accounts, 62% were thought likely to be linked to overseas users, while the authentic accounts surveyed were more likely to be from New Zealand.
A significant proportion of the inauthentic accounts were associated with the United States and the summary suggested that it might have been because there was less scrutiny towards them from Facebook.
Some inauthentic accounts regularly spread international anti-vaccination commentary and promoted online disinformation, while others liked posts and comments.
In its assessment, the Osint team argued it was possible the fake accounts could make users of the groups believe they were part of a larger movement than they actually were, promote misinformation, agitate users and "promote lawbreaking through posting incitement or interacting with similar posts".
A screenshot of a post encouraging thousands of group members to turn up to Parliament to demand action against a corrupt government controlled by "a group of people conspiring against the worlds population," was taken from one of the groups and included in the report.
A Facebook group which was not linked to anti-vaccination messages — NZ Organic Gardening, , which had 12,200 members — was selected as a control group.
Out of 200 accounts looked at, just four were thought to be inauthentic.
